ChemistryA moodily lit Manhattan loft—populated by chefs carrying hors d'oeuvres—isn't the setting one would expect for a swingers party, but the crowd here would only use that term ironically. Chemistry is a leader of the new crop of young, hip sex parties in the city. I'm at their Biochemistry night, which is a fluid, bisexual affair.

As couples from their twenties to early forties fill the two-floor loft space, everyone's abuzz with anticipation—pumping straws in and out of their cocktails. A soulful-house DJ builds anticipation, and partygoers softly bump into one another.

Upstairs, the floor is covered with futons, and a thin, exotically dressed woman advertises tantric massages in the corner. The first person to get naked is a tall, strikingly handsome man in his early thirties who buys a rubdown.

Watching him, two people undress and fall onto the futons, getting into rough and fast missionary sex. Waves of couples and threesomes follow, with some of the 15-odd people upstairs watching and gauging how they could get involved.

One woman moans and convulses while three people massage and tease her with vibrators. An attractive foursome, propped up next to the massage table, take turns pleasuring one person in the group, slowly rubbing, licking and sucking before switching.

Downstairs, a few people in various states of undress dance to the DJ. Later, burlesque acts draw a crowd and applause. It's easy to lose track of the outside world since cell phones must be checked at the door, but at 3:30am, the tangles of group sex are undone by last call, and smiling, endorphin-saturated patrons spill out onto the street. Location revealed to members; apply at chemistry-nyc.com. Single women and couples only, with limited exceptions. Next party Oct 1; single females $12--$25, couples $90--$130

More sex parties

Behind Closed DoorsThe vibe at these monthly Manhattan orgies is elegant—more cocktail lounge than dance party. There's no BDSM or kink, just hot group sex. The parties are held in private venues (lofts, suites, townhouses), and before things get under way, there's a women-only mixer called Girls Uncorked, followed by Swing School, a primer on the lifestyle. Single ladies get extra attention from couples here—sorry, no single males allowed. While the organizers claim models and celebs attend, a sliding price scale makes it accessible to cute students as well. Registered users can use the code TONY25 at checkout to receive 25 percent off ticket prices for parties through Dec 31. Location and date vary; visit schoolofsex.net for details and to register. Single females $50, couples $160.

Myth PartyThese events are among the youngest, kinkiest and most queer-friendly in the city: The last one boasted a human piata (it's what you think it is), a pee-play section, unicorn activities and a Dexter scene in which participants were drenched in fake blood. While the vast majority of partygoers are young (it's 21-plus), one of the few older attendees, a man in his sixties, commented that the scene was a throwback to the anything-goes '70s. It's all about trying whatever kink you can dream up. However, the kids at this party take consent berseriously; they'll kick you out if you don't ask before you touch. Register at mythpartynyc.com for location and date of the next party. $5--$15.

Lip ServiceGames like Spin the Bottle help get things going at House of Scorpio's kissing parties, where corners are filled with people cuddling, kissing and letting their hands roam. Jaded veterans of the scene may roll their eyes at the vanilla couples giggling about how naughty they feel, but the gathering fulfills junior-high make-out-party fantasies, and because there's no intercourse, it's low risk. (That does mean you may have to say "no thanks" more often—it's not as hard to ask someone for a kiss.) The party uses the Kinky Salon--developed PAL (Pervy Activity Liaison) system: You must come with a friend (or two), and your acquaintance doesn't have to be your partner. Just dress creatively—think bohemian, glitter-punk or pinup—the doorman will turn you away if he doesn't like your outfit. Madame X, 94 W Houston St between La Guardia Pl and Thompson St (houseofscorpio.com). Oct 7 at 10pm; $12, with R.S.V.P. via House of Scorpio's website. $8.

One Leg UpThis event's keywords are sensual and sophisticated: Organizers screen prospective partygoers carefully, selecting beautiful people and Manhattan-professional types. There are two kinds of soirees: Take Out (single females $20, couples $100) is a meet-and-greet that keeps things R-rated; at Eat In events (single females $50, couples $250), you can expect many flavors of debauchery. (Past parties have incorporated magicians, jugglers, aerialists and body painters.) For themed events, like the upcoming Studio 54 soiree, all attendees must dress the part. OLU has a strict couples- and single-females--only policy, though single males are admitted on rare occasion. Location, date and price varies; visit onelegupnyc.com for details.